This invention relates generally to improvements in prosthetic devices, particularly such as hip prostheses and the like. More particularly, this invention relates to an improved hip prosthesis designed for improved noncemented fixation with patient bone, while permitting relatively easy removal of the prosthesis, if required.
Artificial or prosthetic devices for implantation into animals, particularly humans, have been the subject of extensive research and development efforts for many years. Such prosthetic devices have typically comprised one or more implant components formed from a relatively biostable material having selected structural properties and unique shapes to replace all or part of selected bone structures, such as an anatomical joint including, for example, a hip or knee joint. The implant components are installed by surgical access to the subject bone or joint region and by resection of one or more bone surfaces to accommodate direct implant component attachment thereto. In the past, this bone attachment has been commonly achieved by use of bone cements, such as a methyl methacrylate based cement or the like, with the cement interdigitating within the interstices of bone surfaces to achieve mechanical fixation at the bone-cement interface.
In recent years a variety of potential disadvantages or limitations have been recognized with respect to cemented fixation of prosthetic devices. More particularly, it has been generally recognized that the use of bone cement to fixate implant components provides a temporary securement which normally requires significant restrictions upon postoperative patient activity to avoid failure of the cemented interface during the patient's lifetime. Failure of the cemented interface is especially undesirable, since the bone cement contributes to a significant degree of localized bone structure loss which makes implantation of a secondary replacement prosthesis extremely difficult and frequently impossible. The problems encountered by use of cemented prosthetic devices are particularly severe with high load bearing, highly stressed joints, such as a hip joint.
In an effort to avoid use of bone cements, a variety of improved prosthetic devices have been proposed for noncemented attachment to resected bone surfaces. Some of these noncemented devices have suggested the use of attachment surfaces having closely control porosity characteristics designed to accommodate direct bone attachment by ingrowth or resorption of living cancellous bone or tissue. However, while these bone ingrowth proposals appear to offer significant advantages over prior cemented designs, various problems have still been encountered with respect to insuring a positive and stable prosthesis fixation particularly at highly loaded and stressed joints, such as the hip. For example, slight subsidence of the prosthesis-supporting bone during normal postoperative patient function can result in permanent loosening and eventual failure of the prosthesis. However, subsequent surgical removal of the failed prosthesis can be extremely difficult and/or impossible.
There exists, therefore, a significant need for an improved prosthetic device particularly adapted for use as a hip joint, wherein the prosthesis is designed for noncemented fixation to patient bone and to withstand high loading and stress to provide a prolonged service life. In addition, in the event of prosthesis failure for any reason, there exists a need for an improved prosthesis which can be removed relatively easily for replacement with an appropriately sized secondary prosthesis. The present invention fulfills these need and provides further related advantages.